The ground has been shaking so regularly in Parker and Tarrant counties, including another quake on Tuesday, that the Azle school district has taken the unusual step of conducting earthquake drills.

Before the Thanksgiving holiday, all 10 campuses had a drill.

“Most of us live in Azle,” said district spokeswoman Tanya Anderson. “We knew [the quakes] were happening. We anticipated there would be concerns from some in our community.”

In the schools’ “drop, cover and hold” drills, “basically, you go to the ground and cover your head,” Anderson said.

Tuesday’s quake at 9:44 a.m. was a magnitude 2.7 centered one mile east-southeast of Reno and 2 miles north of Azle, the U.S. Geological Survey reported. Quakes now number at least 20 since Nov. 1. Most have been in northeast Parker County near the Azle-Reno area.

The Azle schools drills are just one indication of concern about the outbreak of quakes.

“I’m starting to get a lot more phone calls and emails about it,” said Azle Mayor Alan Brundrett.

The only quake he personally felt was the 3.6 quake on Nov. 19 that occurred while he was in a City Council meeting

“It was just a jolt,” Brundrett said. “It was like somebody came by and kicked your chair.”

In the absence of an explanation for the unusual seismic activity, speculation has turned to whether injection wells, part of the natural gas drilling process, might be a cause.

“In my opinion, if the quakes are caused by injection wells, then they need to stop,” Brundrett said.

But there is little the city can do to investigate injection wells, he said. Most of the wells are outside city limits and fall under the jurisdiction of the Texas Railroad Commission.

Ramona Nye, a Railroad Commission spokeswoman, said the agency “is closely following various studies that are being conducted to determine possible manmade causes of recent seismic events.”

But no connection has been found, she said.

“When earthquakes are reported, our staff will determine if saltwater disposal wells are nearby and then inspect the facilities to ensure that they are in compliance with their Railroad Commission permit conditions,” Nye said. “Please keep in mind, that some reported earthquake epicenters in Texas have not been near saltwater disposal or injection wells.”

Last week, railroad commission staffers “inspected one Azle-area disposal well after the reported seismic events and found this disposal well was in compliance with commission rules,” Nye said.

The series of quakes have prompted dam inspections by both the Tarrant Regional Water District and the Brazos River Authority, but no problems have been found.

“We’ve been closely monitoring instrumentation at the [Eagle Mountain Lake] dam and conducting daily visual inspection over the last few weeks,” said water district spokesman Chad Lorance. “We’ve seen no change in the structure’s foundation or embankment.”

The 80-year-old dam was recently upgraded to bring it in line with current design standards.

Farther west, the Brazos River Authority said it had conducted five inspections over the last week, including one on Monday, to check on the integrity of the Possum Kingdom Lake dam, which was built in 1941. The authority experts inspect a dam anytime a quake occurs in a 60-mile radius.

“We want to assure everyone that the dam is safe,” said Judi Pierce, an authority spokeswoman.

The Possum Kingdom dam was upgraded in the mid-1980s, Pierce said, and officials have seen no signs of damage or movement in the dam. The authority has also been monitoring the dam at Lake Granbury.

Both the Brazos River Authority and the Tarrant water district have emergency action plans if any problems are discovered.